The present invention relates generally to optical networks and more particularly relates to a virtual bi-directional connection system for connecting unidirectional devices to other bi-directional devices.
Optical communication systems are becoming increasingly widespread due mainly to the very large bandwidths they offer for carrying information. The growth and diversity of lightwave networks, such as Wavelength Division Multiplexed (WDM) and Dense WDM (DWDM) networks are placing new demands on all aspects of optical networks including, for example, capacity management and provisioning, maintenance, and reliable and robust operation.
Currently, high capacity optical networks are constructed as rings and use WDM technology to achieve high bandwidth capacities. For example, WDM ring networks are in commonly used in metropolitan area network (MAN) applications but can also be used in LANs and WANs.
Wavelength division multiplexed (WDM) optical networks are particularly desirable because of their restoration capabilities and suitability for minimizing the number of optical fibers for the interconnection of system nodes. A typical WDM optical ring network includes network elements with optical add/drop multiplexers (OADMs), whereby some optical channels are dropped, some are added and/or other channels are expressed or passed through.
In a ring topology, each ring node is connected to exactly two other ring nodes. The OADMs are used to construct a ring network whereby adjacent OADMs are connected pair wise while the network nodes are adapted to form a ring. In a ring network, any node can be reached from any other node using two physically separate paths, i.e. one traveling clockwise and one counter clockwise. This is used for providing protection against route failures. The use of at least two parallel fibers with traffic flowing in opposite directions provides restoration capabilities in the event of a fiber cut.
An Optical Add/Drop Multiplexer (OADM) functions to filter or drop one or more wavelengths transiting on the ring. The optical technologies usable for producing an OADM can be placed in two main categories, namely: (1) those using fixed filtering, whereby an OADM is produced for dropping and adding a fixed wavelength, and (2) those using tunable filtering, whereby an external control determines the wavelength of the dropped and added channel.
Normally, only a single wavelength of light is used to carry optical signals from one node to another. To increase the communications bandwidth of the network, however, it is common to transmit light signals having multiple wavelengths. Additional signal channels can be added using well-known DWDM techniques wherein each channel corresponds to a different wavelength of light.
As is common practice in DWDM optical networks, OADMs are used to drop, add or express one or more optical channels. The OADM comprises a drop module adapted to generate a drop channel from the multi-wavelength input signal and an add module adapted to add a channel to the multi-wavelength output signal.
Many of the optical based devices and components used to construct optical networks function to process an input optical signal to generate an output optical signal. Both input and output optical signals (i.e. ingress and egress signals) comprise separate signals for both transmit and receive directions. A diagram of an example prior art optical networking rack having a plurality of optical networking cards is shown in FIG. 1. The optical card cage, generally referenced 10, comprises a plurality of slots for optical circuit cards. Two are shown to illustrate the typical connections that occur between processing cards. Bi-directional processing cards 12, 14, labeled circuit card A and circuit card B, comprise input ports 16 and output ports 22. The input port comprises individual transmit (Tx) 18 and receive (Rx) 20 ports. Similarly, the output port 22 comprises individual transmit 24 and receive 26 ports.
To connect one processing card to another, a pair of cables 28, 30 is used to connect the transmit and receive ports from the output port of one card to the input port of the card in the downstream processing path. More particularly, one cable 28 functions to connect the output transmit port of one card to the input receive port of the downstream card. The second cable 30 functions to connect the output receive port of one card to the input transmit port of the downstream card. In this manner, the various bi-directional optical processing cards are connected together.
One way to connect the ports from one card to another is to use individual optical fiber cables for each pair of connections. Great care must be given to connecting each cable to the correct port An alternative is to use a special paired cable that is keyed on each end. A diagram of a prior art bi-directional optical cable including keyed transmit and receive optical fiber connections is shown in FIG. 2. The cable, generally referenced 40, comprises keyed connectors 44 on each end of a pair of optical fiber cables 46, 48. The cables are crossed to insure that a transmit port is connected to a receive port and vice versa. A key 44 comprising a tab or other keying mechanism is used to guarantee that the orientation of the cable is correct when a user connects the cable to the port
A block diagram of example prior art bi-directional optical circuit cards connected together via a keyed cable comprising transmit and receive fibers is shown in FIG. 3. The example system, generally referenced 50, comprises two optical circuit cards 52, labeled circuit card A and circuit card B, connected via keyed optical pair cable 60. Each circuit card is a bi-directional processing circuit card having a processing circuit 56, an input port 54 and output port 58. Each port further comprises transmit and receive connections. During installation of the cards, a user manually connects the output port of circuit card A to the input port of circuit card B. To insure the correct orientation of the connections, the keyed cable is used which forces the user to properly connect the ports together. As long as a keyed cable is used, the transmit port of one card will always be connected to the receive port of the other card. Likewise, the receive port of one card will always be connected to the receive port of the other card.
A problem arises, however, when connecting unidirectional processing cards to other processing cards in the system. The problem is that unidirectional cards only process signals in one direction. These types of cards only have a single input and output which force the user to apply great care when connecting them in a system. This problem is illustrated in FIG. 4 which shows a block diagram of several prior art optical circuit cards that include both bi-directional and unidirectional devices.
The system, generally referenced 70, comprises two bi-directional processing cards 72, labeled circuit card A and circuit card B, connected to a unidirectional processing card 80. Circuit cards A and B comprise a processing circuit 78 and input ports 74 and output ports 76, each comprising transmit and receive connections. The unidirectional card in this example is an amplifier card having only an input receive port 84 connected to the output transmit port of circuit card A via optical cable 88 and an output transmit port 86 connected to the input receive port of circuit card B via optical cable 90.
Since the amplifier card functions to only process the signal output of card A the input transmit signal from circuit card B is connected directly to the output receive port of circuit card A via optical cable 92. Thus, cable 92 is connected so as to bypass the amplifier card altogether. A problem with this arrangement, however, is that standard keyed optical cables cannot be used since the amplifier card does not process optical signals in both directions. Thus, great care must be exercised by the user when connecting the circuit cards together that include one or more unidirectional devices such as amplifiers, etc. If the proper care is not exercised, improper connection between the input and output parts on the processing cards will result thus preventing the proper operation of the network system or potentially causing damage to one or more components in the optical system.
There is thus a need for a connection scheme for optical networking devices employing unidirectional processing cards that permits the use of keyed optical cables to insure the proper connection of the input and output ports of the various processing cards making up the system.
The present invention is a connection mechanism permit a unidirectional processing device to function as a virtual bi-directional processing device. The invention has applications in any device that employs a unidirectional processing element, such as a circuit card. Use of the invention enables unidirectional processing cards to be connected to bi-directional cards using standard keyed cable assemblies. The invention can be used in both optical and electrical processing card environments. In particular, the invention is suited for use in unidirectional optical processing cards such as these comprising Erbium Doped Fiber Amplifiers (EDFAs) or dispersion compensation modules (DCMs).
In accordance with the present invention, a dummy connection is inserted in the circuit card to permit the connection of standard paired cable assemblies. The standard paired cables may or may not be keyed. The use of keyed cables to connect the various circuit cards in a system reduces the responsibility of a user to insure that the cables are properly connected since keyed cables only allow installation in one way, the correct way. The dummy connection is a passive connection that may comprise any suitable media type such as optical or electrical.
Implementation of the virtual bi-directional connection mechanism of the present invention does not require modification of the unidirectional processing elements on a circuit card. Conventional unidirectional processing elements may be used unchanged. An additional output receive terminal and input transmit terminal are added and the two connected internally by the dummy connection.
A key advantage of the present invention is that it enables unidirectional processing cards to be connected as if they were bi-directional processing cards thus permitting the use of standard keyed cable assemblies in connecting them to other processing cards.
There is thus provided in accordance with the present invention an apparatus for use in a unidirectional processing card having an input receive port and an output transmit port comprising an output receive port, an input transmit port and dummy connection means for connecting the output receive port to the input transmit port.
There is also provided in accordance with the present invention a virtual bi-directional processing apparatus comprising an input port comprising a transmit connector and a receive connector, an output port comprising transmit connector and a receive connector, a unidirectional optical processing element connected between the receive connector of the input port and the transmit connector of the output port and a dummy optical fiber connecting the receive connector of the output port to the transmit connector of the input port.
There is further provided in accordance with the present invention an optical network device comprising a plurality of bi-directional processing cards each having a first input port with transmit terminal and receive terminal and a first output port with transmit terminal and receive terminal, one or more unidirectional processing cards each having a second input port with transmit terminal and receive terminal and a second output port with transmit terminal and receive terminal and wherein each one or more unidirectional processing cards comprises a unidirectional processing element coupled between the receive terminal of the second input port to the transmit terminal of the second output port and a dummy optical fiber connecting the receive terminal of the second output port to the transmit terminal of the second input port.